With the advent of low-cost microprocessors, pen plotters with high speed and resolution have become increasingly sophisticated. Such pen plotters, which are usually driven by command from an external computer, include means for supporting paper or other ink receiving media, a mechanism for moving the paper or other ink receiving media back and forth during plotting, a carriage which supports a pen during the plotting operation, a mechanism for moving the carriage normal to the movement of the paper during plotting, a pen turret for storing a plurality of pens for use in plotting, and a mechanism for rotating the turret.
The use of a pen turret permits utilization of a plurality of pens, such as different colors, different pen tip widths, and the like to provide a variety of pen plots. The microprocessor permits the operator to select the sequence of pens to be used in the plot and then drives the pen turret motor at the appropriate time to rotate the turret when a particular pen is to be selected therefrom.
U.S. Pat. No. 4,417,258, which issued on Nov. 22, 1983 to Tribolet et al., discloses a bidirectional pen chanber in which a pen carriage with gripping claws snatches a pen from a pen stable with cooperating claws for use in drawing, then returns the pen to its stable after use. A plurality of pen stables may be placed at either end of the slider rod for the pen carraige, and the pen stables may be translated perpendicularly to the pen carriage for selective engagement with the pen carriage.
U.S. Pat. No. 4,573,129 which issued on Feb. 25, 1986 to Tribolet et al., discloses how to determine the presence or absence of plotting pens by the use of cooperating claws and an initialization routine that is run whenever the plotter is powered on. This technique works without the use of mechanical switches or optical sensors.
U.S. Pat. No. 4,716,420, which issued on Dec. 29, 1987 to Glassett, discloses a typical prior art arrangement in which a rotatable turret supplies a variety of pens to the pen carriage. This patent also discloses how to rotate the turret without the need of a motor solely for this purpose.
U.S. Pat. No. 4,533,924, which issued on Aug. 6, 1985 to Takahashi, discloses a plotter pen assembly in which an assortment of is part of, and moves with the pen carriage.
These prior art plotters work well for their intended purposes, but each requires that a human operator be present to replace spent pens with fresh ones.